Acrylic powder coating resin having low volatility

ABSTRACT

Powder coating compositions having reduced volatility and improved processibility compared to conventional powder coatings consist essentially of a copolymer having pendant functionalities or pendant groups capable of reacting with a dicarboxylic acid such as the glycidyl groups of glycidyl acrylate or methacrylate copolymer and a cross-linking effective amount of a dicarboxylic acid. The reaction of the above pendant groups and the dicarboxylic acid cross-links or cures the powder coating after application to a substrate. The dicarboxylic acids according to the invention eliminate the need for a third component which is a flow control agent which improves the processibility of a two-component powder coating. The dicarboxylic acids according to the invention have a sublimation temperature great enough to decrease or prevent their vaporization during the curing of the powder coating and have a melting point low enough to impart improved flow properties to the powder coatings.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of copending provisionalapplication serial No. 60/274,966, filed on Mar. 12, 2001, the entirecontents of which are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] Thermosetting powder coatings have gained considerable popularityin recent years over liquid coatings for a number of reasons. Powdercoatings are virtually free of harmful volatile organic compounds (VOC)normally present in liquid coatings, and, as a result, give off little,if any, volatiles to the environment when cured. This eliminates solventemission problems and dangers to the health of workers employed in thecoating operations. Powder coatings also improve working hygiene, sincethey are in dry solid form with no messy liquids associated with them toadhere to workers' clothes and coating equipment. Furthermore, they areeasily swept up in the event of a spill without requiring specialcleaning and spill containment supplies. Another advantage is that theyare 100% recyclable. Over-sprayed powders are normally recycled duringthe coating operation and recombined with the original powder feed. Thisleads to very high coating efficiencies and minimal waste generation.

SUMMARY OF THE INVENTION

[0004] The present invention relates to a powder coating compositionhaving reduced volatility and improved processibility compared toconventional powder coatings. The powder coating composition accordingto the invention consist essentially of a copolymer having pendantfunctionalities or pendant groups capable of reacting with adicarboxylic acid such as the glycidyl groups of glycidyl acrylate ormethacrylate copolymer and a cross-linking effective amount of adicarboxylic acid. The reaction of the above pendant groups and thedicarboxylic acid cross-links or cures the powder coating afterapplication to a substrate. The dicarboxylic acids according to theinvention eliminate the need for a third component which is a flowcontrol agent which improves the processibility of a two-componentpowder coating. The dicarboxylic acids according to the invention have asublimation temperature great enough to decrease or prevent theirvaporization during the curing of the powder coating and have a meltingpoint low enough to impart improved flow properties to the powdercoatings.

DETAILED DESCRIPTION OF THE INVENTION

[0005] The copolymer having pendant functionalities capable of reactingwith a dicarboxylic acid according to the invention can be any copolymerthat is suitable for use in powder coating compositions and alsocontains pendant functionalities capable of reacting with the carboxylgroup of a carboxylic acid. Functionalities capable of reacting with thecarboxyl group of a carboxylic add include, but are not limited to,epoxides, alcohols, amines, thiols, and carboxylic acids.

[0006] The copolymers according to the invention include, but are notlimited to, acrylate and methacrylate copolymers of glycidyl acrylateand methacrylate as described in U.S. Pat. No. 3,752,870, the entirecontents of which are incorporated herein by reference. Other examplesof copolymers include those containing hydroxyethyl and hydroxypropylpendant functionalities such as copolymers of acrylic and methacrylicesters and 2-hydroxyethyl acrylate and/or methacrylate and acrylic andmethacrylic esters and 2-hydroxypropyl acrylate and/or methacrylate. Thepreferred copolymer is one that contains glycidyl acrylate and/orglycidyl methacrylate.

[0007] The dicarboxylic acids useful in the compositions according tothe invention are dicarboxylic acids having at least 14 carbon atoms,preferably saturated dicarboxylic acids having from about 14 to about 20carbon atoms. Such dicarboxylic acids can be prepared by standardchemical methods known to those of ordinary skill in the art and bybiooxidation of the corresponding alkane or mono carboxylic acid such asis described in U.S. Pat. No. 5,254,466, the entire contents of whichare incorporated herein by reference. The amount of dicarboxylic acidthat can be used in the compositions according to the invention is across-linking effective amount which is defined as any amount necessaryto cure the powder coating to a desired level. The effective amount willvary and will be readily determinable by one of ordinary skill in theart. Typically, the effective amount will range from about 2% by weightto about 50% by weight of copolymer. The preferred dicarboxylic acid isoctadecanedioc acid.

[0008] The powder coating compositions according to the inventionexhibit reduced volatility and improved processibility compared toconventional powder coatings and do not require the incorporation of aflow control agent to reduce or eliminate the rough flow out of themolten powder coating film that results after the powder coating isapplied and heated.

[0009] The following examples are meant to illustrate but not to limitthe invention.

EXAMPLE 1 Powder Coatings Compounding Method

[0010] A series of powder coatings were compounded to evaluate C9, C10,C12, C13, C15, and C18 dibasic acids as curing agents in GMA acrylicresin. The powder coatings were prepared using equal weight percent andapproximate molar amounts of dibasic acids compounded with Fine Clad®A207-SA GMA acrylic resin. All powder coatings were compounded using aBrabender No. 6 roller head operating at 50 rpm with a startingtemperature of 80° C. and not exceeding 93° C. for approximately 15minutes to achieve intimate mixing. All powder coating compounds wereground to a fine powder and are identified in Table 1. Table 1 GMAAcrylic Resin Dibasic Acid Sample No. Dibasic Acid Grams Grams 00078-173C9 34.71 5.29 00078-174 CIO 34.38 5.62 00078-175 C12 33.6 6.4 00078-176C13 33.21 6.79 00078-177 CIS 32.43 7.57 00078-178 Cia 31.32 8.6800078-190 Cia 33.6 6.4 00078-191 C15 33.6 6.4 00078-192 C13 33.6 6.400078-193 C12 33.6 6.4 00078-194 dO 33.6 6.4 00078-195 C9 33.6 6.4

EXAMPLE 2 Inclined Flow and Stability

[0011] Inclined flows were performed on the powder coatings aftercompounding and grinding to a fine powder to determine initial inclinedflow characteristics. Subsequent inclined flows were performed over theindicated periods of time to determine the stability of each powdercoating. The inclined flow data is listed in the following tables. Thepowder coatings were evaluated for inclined flow performance at 120° C.and 150° C. using the following method. About 80 milligrams of eachpowder coating was placed “side by side” onto a 3-inch by 5-inch metalsheet. The sheet was placed into a (120° C. or 150° C.) preheatedconvection oven for approximately 2 minutes laying flat. After twominutes, the plate was placed on a 55-60 degree incline for 20 minutes(at 120° C. or 150° C.) for inclined flow and curing. After the20-minute flow and cure period, each cured powder coating flow wasevaluated for flow length. Each flow length was determined by measuringfrom a reference line drawn parallel to the powder coatings on eachmetal plate.

[0012] Initial inclined flow evaluations were performed on laboratoryprepared powder coatings at 120° C. and 150° C. shortly aftercompounding. Additional inclined flows were performed approximately 150days after the initial inclined flows to determine room temperaturestability.

[0013] The inclined flows indicate that Sample 00078-178 (contains C18diacid) has greater flow at 150° C. and superior stabilitycharacteristics at 120° C. and 150° C. Sample 00078-177 (contains C15diacid) appears to have better initial flow characteristics at 120° C.as shown in Table 2. TABLE 2 120° C. 150° C. 120° C. Flow 150° C. FlowFlow After 151 Flow After 152 Initial days % Decrease Initial days %Decrease Sample No. Inches Inches In Flow Inches Inches In Flow00078-173 (C9) 0.5 No flow 100 0.75 No flow 100 00078-174 (C10) 0.5 0.3530 0.875 0.5 42 00078-175 (C12) 0.75 0.65 13 1.06 0.75 29 00078-176(C13) 0.875 0.8 9 1.25 0.8 36 00078-177 (C15) 1.25 1.1 12 1.4 1.1 2100078-178 (C18) 1.1 1.1 0 1.5 1.45 3

EXAMPLE 3 Inclined Flows of GMA Acrylic Resin Compounded with EqualWeight Percent Amounts of Dibasic Acid Stored at Room Temperature

[0014] Initial inclined flow evaluations were performed on laboratoryprepared powder coatings at 120° C. and 150° C. shortly aftercompounding. Additional inclined flows were performed 71 days after theinitial inclined flows to determine room temperature stability. Theresults are shown in Table 3. The samples are identified by thedicarboxylic acid contained therein. For example, sample 00078-195 (C9)is a GMA Acrylic Resin Compounded with azelaic acid. TABLE 3 120° C.150° C. 120° C. Flow 150° C. Flow Flow After 71 Flow After 71 Initialdays % Decrease Initial days % Decrease Sample No. Inches Inches In FlowInches Inches In Flow 00078-195 (C9) 0.6 0.1 83 0.6 0.1 83 00078-194(C10) 0.65 0.55 15 0.85 0.65 23 00078-193 (C12) 0.75 0.7 6 1.0 0.8 2000078-192 (C13) 0.8 0.7 12 0.95 0.75 21 00078-191 (C15) 1.0 0.95 5 1.150.9 21 00078-190 (C18) 0.9 0.9 0 1.2 1.05 12

EXAMPLE 4 Inclined Flows of GMA Acrylic Resins Compounded withApproximate Molar Amounts of Dibasic Acid Stored at 35° C.

[0015] Approximately 10 grams of Sample 00078-175 and 00078-178 wereplaced in a 35° C. oven 89 days after initial inclined flow evaluationshown in Table 2. Each sample was evaluated for inclined flow after theindicated period of time identified in Table 4. TABLE 4 150° C. FlowStored % Decrease in 150° C. Flow Stored 36 Days at Flow 6 Days at 35°C. 35° C. From Day 6 to Sample No. Inches Inches Day 36 00078-175 0.750.2 73 (C12) 00078-178 1.5 1.35 10 (C18)

EXAMPLE 5 Inclined Flows of GMA Acrylic Resin Compounded with EqualWeight Percent Amounts of Dibasic Acid Stored at 35° C.

[0016] Approximately 10 grams of Sample 00078-193 and 00078-190 wereplaced in a 35° C. oven 1 day after initial inclined flow evaluationshown in Table 3. Each sample was evaluated for inclined flow after theindicated period of time identified in Table 5. TABLE 5 150° C. 150° C.Flow Flow Stored % Decrease Stored 6 Days at 61 days at in Flow From 35°C. 35° C. Day 6 to Day Sample No. InChes Inches 61 00078-193 0.75 0.3 60(C12) 00078-190 1.0 0.75 25 (C18)

What is claimed is:
 1. A composition consisting essentially of acopolymer having a pendant functionality capable of reacting with adicarboxylic acid and a cross-linking effective amount of a dicarboxylicacid having at least 14 carbon atoms.
 2. The composition of claim 1wherein the dicarboxylic acid is a saturated dicarboxylic acid.
 3. Thecomposition of claim 1 wherein the dicarboxylic acid has from about 14to about 20 carbon atoms.
 4. The composition of claim 2 wherein thedicarboxylic acid is octadecanedioic acid.
 5. The composition of claim 1wherein the copolymer is a glycidyl methacrylate or a glycidyl acrylatecopolymer.
 6. The composition of claim 1 wherein the effective amount ofthe dicarboxylic acid is from about 2% to about 50% by weight.
 7. Acomposition consisting essentially of a copolymer having glycidylpendant groups and a cross-linking effective amount of octadecanedioicacid.
 8. A composition consisting essentially of a glycidyl methacrylateand an effective amount of octadecanedioic acid.
 9. A compositionconsisting essentially of a glycidyl methacrylate and from about 2% toabout 50% by weight of octadecanedioic acid.